Duration of buff is 60 minutes and is applied to the character, not the mount.

If you have a Brewfest Hops buff active and want to apply a different Brewfest Hops buff, the other faction's mount, for example, the current buff blocks application of the new buff. You must manually turn off the current buff by right clicking it and dispelling it in order to apply the new buff. (Source)

The act of consuming the item awards the achievement Have Keg, Will Travel. Players do not need to own a mount, mount up, or even have trained in riding. (Note: Characters must, however, be eligible to learn Riding - so characters must be at least level 20.)